git-update-ref - Man Page

• Delete a ref, useful for soft resetting the first commit: git update-ref -d HEAD
• Update ref with a message: git update-ref -m message HEAD 4e95e05

tldr.sh

git update-ref [-m <reason>] [--no-deref] -d <ref> [<old-oid>]
git update-ref [-m <reason>] [--no-deref] [--create-reflog] <ref> <new-oid> [<old-oid>]
git update-ref [-m <reason>] [--no-deref] --stdin [-z] [--batch-updates]

Given two arguments, stores the <new-oid> in the <ref>, possibly dereferencing the symbolic refs​. E​.g​. git update-ref HEAD <new-oid> updates the current branch head to the new object​.

Given three arguments, stores the <new-oid> in the <ref>, possibly dereferencing the symbolic refs, after verifying that the current value of the <ref> matches <old-oid>​. E​.g​. git update-ref refs/heads/master <new-oid> <old-oid> updates the master branch head to <new-oid> only if its current value is <old-oid>​. You can specify 40 "0" or an empty string as <old-oid> to make sure that the ref you are creating does not exist​.

The final arguments are object names; this command without any options does not support updating a symbolic ref to point to another ref (see git-symbolic-ref(1))​. But git update-ref --stdin does have the symref-* commands so that regular refs and symbolic refs can be committed in the same transaction​.

If --no-deref is given, <ref> itself is overwritten, rather than the result of following the symbolic pointers​.

With -d, it deletes the named <ref> after verifying that it still contains <old-oid>​.

With --stdin, update-ref reads instructions from standard input and performs all modifications together​. Specify commands of the form:

update SP <ref> SP <new-oid> [SP <old-oid>] LF
create SP <ref> SP <new-oid> LF
delete SP <ref> [SP <old-oid>] LF
verify SP <ref> [SP <old-oid>] LF
symref-update SP <ref> SP <new-target> [SP (ref SP <old-target> | oid SP <old-oid>)] LF
symref-create SP <ref> SP <new-target> LF
symref-delete SP <ref> [SP <old-target>] LF
symref-verify SP <ref> [SP <old-target>] LF
option SP <opt> LF
start LF
prepare LF
commit LF
abort LF

With --create-reflog, update-ref will create a reflog for each ref even if one would not ordinarily be created​.

With --batch-updates, update-ref executes the updates in a batch but allows individual updates to fail due to invalid or incorrect user input, applying only the successful updates​. However, system-related errors—such as I/O failures or memory issues—will result in a full failure of all batched updates​. Any failed updates will be reported in the following format:

rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF

Quote fields containing whitespace as if they were strings in C source code; i​.e​., surrounded by double-quotes and with backslash escapes​. Use 40 "0" characters or the empty string to specify a zero value​. To specify a missing value, omit the value and its preceding SP entirely​.

Alternatively, use -z to specify in NUL-terminated format, without quoting:

update SP <ref> NUL <new-oid> NUL [<old-oid>] NUL
create SP <ref> NUL <new-oid> NUL
delete SP <ref> NUL [<old-oid>] NUL
verify SP <ref> NUL [<old-oid>] NUL
symref-update SP <ref> NUL <new-target> [NUL (ref NUL <old-target> | oid NUL <old-oid>)] NUL
symref-create SP <ref> NUL <new-target> NUL
symref-delete SP <ref> [NUL <old-target>] NUL
symref-verify SP <ref> [NUL <old-target>] NUL
option SP <opt> NUL
start NUL
prepare NUL
commit NUL
abort NUL

In this format, use 40 "0" to specify a zero value, and use the empty string to specify a missing value​.

In either format, values can be specified in any form that Git recognizes as an object name​. Commands in any other format or a repeated <ref> produce an error​. Command meanings are:

update

Set <ref> to <new-oid> after verifying <old-oid>, if given​. Specify a zero <new-oid> to ensure the ref does not exist after the update and/or a zero <old-oid> to make sure the ref does not exist before the update​.

create

Create <ref> with <new-oid> after verifying that it does not exist​. The given <new-oid> may not be zero​.

delete

Delete <ref> after verifying that it exists with <old-oid>, if given​. If given, <old-oid> may not be zero​.

symref-update

Set <ref> to <new-target> after verifying <old-target> or <old-oid>, if given​. Specify a zero <old-oid> to ensure that the ref does not exist before the update​.

verify

Verify <ref> against <old-oid> but do not change it​. If <old-oid> is zero or missing, the ref must not exist​.

symref-create

Create symbolic ref <ref> with <new-target> after verifying that it does not exist​.

symref-delete

Delete <ref> after verifying that it exists with <old-target>, if given​.

symref-verify

Verify symbolic <ref> against <old-target> but do not change it​. If <old-target> is missing, the ref must not exist​. Can only be used in no-deref mode​.

option

Modify the behavior of the next command naming a <ref>​. The only valid option is no-deref to avoid dereferencing a symbolic ref​.

start

Start a transaction​. In contrast to a non-transactional session, a transaction will automatically abort if the session ends without an explicit commit​. This command may create a new empty transaction when the current one has been committed or aborted already​.

prepare

Prepare to commit the transaction​. This will create lock files for all queued reference updates​. If one reference could not be locked, the transaction will be aborted​.

commit

Commit all reference updates queued for the transaction, ending the transaction​.

abort

Abort the transaction, releasing all locks if the transaction is in prepared state​.

If all <ref>s can be locked with matching <old-oid>s simultaneously, all modifications are performed​. Otherwise, no modifications are performed​. Note that while each individual <ref> is updated or deleted atomically, a concurrent reader may still see a subset of the modifications​.

If config parameter "core​.logAllRefUpdates" is true and the ref is one under "refs/heads/", "refs/remotes/", "refs/notes/", or a pseudoref like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/<ref>" exists then git update-ref will append a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all symbolic refs before creating the log name) describing the change in ref value​. Log lines are formatted as:

oldsha1 SP newsha1 SP committer LF

Where "oldsha1" is the 40 character hexadecimal value previously stored in <ref>, "newsha1" is the 40 character hexadecimal value of <new-oid> and "committer" is the committer’s name, email address and date in the standard Git committer ident format​.

Optionally with -m:

oldsha1 SP newsha1 SP committer TAB message LF

Where all fields are as described above and "message" is the value supplied to the -m option​.

An update will fail (without changing <ref>) if the current user is unable to create a new log file, append to the existing log file or does not have committer information available​.

Symbolic refs were initially implemented using symbolic links​. This is now deprecated since not all filesystems support symbolic links​.

This command follows real symlinks only if they start with "refs/": otherwise it will just try to read them and update them as a regular file (i​.e​. it will allow the filesystem to follow them, but will overwrite such a symlink to somewhere else with a regular filename)​.

git-symbolic-ref(1)

Part of the git(1) suite